The ADC Pi Zero is an 8 channel 17 bit analogue to digital converter designed to work with the Raspberry Pi Zero. The ADC Pi Zero is based on two Microchip MCP3424 A/D converters each containing 4 analogue inputs. The MCP3424 is a delta-sigma A/D converter with low noise differential inputs.

We designed the ADC Pi Zero to work as a single ended A/D converter using the internal 2.048V reference voltage with the -V pins tied to ground. A voltage divider on the ADC Pi Zero board brings the input voltage range to a much more useful 0 – 5.06V. In this configuration the sample size is 17 bits for each channel.

The ADC Pi Zero is powered through the host Raspberry Pi Zero using the GPIO port and extended pins on the GPIO connector allow you to stack the ADC Pi Zero along with other expansion boards.

The two MCP3424 A/D converters communicate via i2c to the host Raspberry Pi giving you eight analogue inputs to use. A logic level converter is included on the ADC Pi Zero board giving you a buffered 5V i2c port making it easy to add other I2C devices which operate at 5 volts without damaging the raspberry pi 3.3 volt i2c port. The i2c buffer uses N-channel mosfets with a maximum drain current of 100mA.

The I2C address bits are selectable using the on-board jumpers. The MCP3424 supports up to 8 different I2C addresses so with two A/D converters on each ADC Pi Zero you can stack up to 4 ADC Pi Zero boards on a single Raspberry Pi Zero giving you 32 ADC inputs.

The MCP3424 contains a programmable Gain Amplifier giving the user a selectable gain of x1, x2, x4 or x8 before the analogue to digital conversion takes place.

The data rate for analogue to digital conversions is 3.75 (17 bit), 15 (15 bit), 60 (13 bit) or 240 (11 bit) samples per second. Data rate and resolution can be configured within software using the I2C interface.

We have a knowledge base article, ADC Sample Rate Comparison which has more detailed sample information and test scripts to compare the different MCP2424 ADC chip bit and sample rates.

Unused inputs should be tied to ground.

If you want to sample a higher input voltage you can use our ADC Pi Input Voltage Calculator to find the additional resistors and calculation values needed.

Board Layout

Schematic

Mechanical Drawings

Click image to enlarge

Assembly

The ADC Pi Zero is supplied with the 40 pin GPIO connector and the 12 pin address connector unsoldered. We supply the ADC Pi Zero this way because the Raspberry Pi Zero is also supplied without a GPIO header and the ADC Pi Zero could therefore be fitted both above or below the Raspberry Pi Zero.

Before using the ADC Pi Zero you will need to solder both connectors onto the PCB. We suggest soldering the 40 pin GPIO connector first and then the address select connector. Soldering the address select connector first will make it difficult to access the three corner pins on the GPIO connector.

The assembly video for the ADC Pi Plus shows the same steps that are needed to assemble the ADC Pi Zero.

PCB Header Assembly Jig

I2C Address Selection

The MCP3424 analogue to digital converter contains two address select pins which can be tied to Vss, Vdd or left floating. This gives 8 possible I2C addresses for each chip. The ADC Pi Zero contains two MCP3424 chips so you can stack up to 4 The ADC Pi Zero boards on a single Raspberry Pi. To simplify address selection on the The ADC Pi Zero we have included a set of address selection pins which can be configured using the included jumpers. The illustrations below show the four recommended configurations for your The ADC Pi Zero and the associated I2C addresses.

Note:
Disconnect the The ADC Pi Zero from the Raspberry Pi before changing the address pins. You may need to short the 5V and ground with a resistor to discharge the capacitors in order for the new addresses to be recognised.

Warning

Do not under any circumstanced connect the two centre pins together. This will create a direct short between the 5V and ground pins and will damage or destroy your Raspberry Pi and ADC Pi Plus board.

Important Information

This development board/kit is intended for use for ENGINEERING DEVELOPMENT, DEMONSTRATION, OR EVALUATION PURPOSES ONLY and is not considered by abelectronics.co.uk to be a finished end-product fit for general consumer use. As such, the goods being provided are not intended to be complete in terms of required design-, marketing-, and/or manufacturing-related protective considerations, including product safety and environmental measures typically found in end products that incorporate such semiconductor components or circuit boards. Persons handling the product(s) must have electronics training and observe good engineering practice standards. This development board/kit does not fall within the scope of the European Union directives regarding electromagnetic compatibility, restricted substances (RoHS), recycling (WEEE), FCC, CE or UL, and therefore may not meet the technical requirements of these directives or other related directives. Note: documents in Portable Document Format (PDF) require Adobe Acrobat Reader 5.0 or higher to view, download Adobe Acrobat Reader or other PDF reading software for your computer or mobile device.